The invention is based on a hydraulic valve control apparatus for an internal combustion engine.
In a known hydraulic valve control apparatus of this generic type (German Published, Non-Examined Patent Application 3 511 820), the pressure line is controlled via a 2/2-way valve; according to a special exemplary embodiment (FIGS. 8 and 9), the multiposition valve connects the pressure line to the pressure chamber of one valve tappet in one switching position, and in the other switching position connects it to the pressure chamber of a different valve tappet, using only a single fluid reservoir for both pressure chambers. Accordingly, for two engine inlet valves, there is one control position each of the magnet valve, and only one reservoir is used for both inlet valves. The precision of control, or in other words how accurately the opening time cross section of the engine valve sought can actually be attained depends, especially at high rpm, on how large the total oil volume is that has to be displaced back and forth during control is, and how many control conduits of corresponding control cross sections have oil flowing through them. The magnet valve is an especially critical factor in the expense and vulnerability to malfunction of a hydraulic valve control apparatus of this kind; with engines having a typical maximum rpm, the possible switching frequency of these magnet valves falls far short of being fully exploited.
It has also already been proposed, (German Patent 38 156 687), in a hydraulic valve control apparatus of this generic type, to embody the reservoir piston as a movable valve element; the face-end edge of the piston cooperates with a valve seat, as a result of which the communication between the pressure line and the reservoir chamber is controllable. The reservoir piston simultaneously serves as the armature of a magnet valve that is open when it is without current, so that when the magnet is excited, the pressure line is disconnected from the reservoir chamber. Although in this version a combination of a fluid reservoir and a magnet valve is disclosed, in which the same element serves as both a movable valve element of the magnet valve and as a reservoir piston, nevertheless this requires that one such magnet valve and reservoir unit must be available for each valve control unit.